How does mercedes electronic car repair history work?

There is no problem to repair at any garage. It is simply not recorded in the mercedes data base.

You can certainly let MB check for a similar problem with your car in the past. Also, it is nice to have a complete service record at MB, but as long as you keep bills for the services of your car, there shouldn't be any problem as loss of value, etc. Again it is simply not stored at MB data base, if the garage has no access to MB data base. Because this access cost some money and most of open garages don't want to pay for data base access of dozens car makers, almost all open garages have no data base access for all the different car makers - even the one that dominate the respective market. The work of open garages are equally valued as the one from brand garages, at least in Europe. There is absolutely no problem to have repairs und service at a garage of your choice. You should just store the bills to have a proof, if necessary.

A mechanic is a mechanic regardless of his present employer.